Molecular gas scaling relations for local star forming galaxies in the low-M_* regime

We derive molecular gas fractions (fₘol=Mₘol/M_*) and depletion times (ₘol= Mₘol/SFR) for 353 galaxies representative of the local star-forming population with 10^8. 5\, M_ < M_* < 10^10. 5\, M_ drawn from the ALLSMOG and xCOLDGASS surveys of CO (2-1) and CO (1-0) line emission. By adding constraints from low-mass galaxies and upper limits for CO non-detections, we find the median molecular gas fraction of the local star-forming population to be constant at fₘol=-1. 04 0. 04 challenging previous reports of increased molecular gas fractions in low mass galaxies. Above M_* 10^10. 5\, M_ we find the M_* vs fₘol relation to be sensitive to the selection criteria for star-forming galaxies. We test the robustness of our results against different prescriptions for the CO-to-H₂ conversion factor and different selection criteria for star-forming galaxies. The depletion timescale ₘol depends weakly on M_*, following a power law with a best-fit slope of 0. 24 0. 03. This suggests that small variations in specific SFR (sSFR=SFR/M_*) across the local main sequence of star forming galaxies with M_* < 10^10. 5\, M_ are driven mainly by differences in the efficiency of converting the available molecular gas into stars. We test these results against a possible dependence of fₘol and ₘol on the surrounding (group) environment of the targets by splitting them into centrals, satellites, and isolated galaxies, and find no significant variation between these populations. We conclude that the group environment is unlikely to have a large systematic effect on the molecular gas content of star-forming galaxies in the local universe.